Radio-frequency identification (RFID) systems are being increasingly deployed to track items for a wide variety of purposes and in a wide variety of environments. For example, RFID systems are increasingly being deployed within supply chains to track inventory from manufacturing through retail distribution, for example. RFID systems are also being utilized to identify and track airline baggage within airports, to identify motor vehicles at toll gates and parking structures, and to track animals and people (e.g., to track animals within an agricultural operation, and to track children at theme parks or other public venues).
RFID systems may of course be deployed in a wide variety of environments, from a factory floor to a theme park. Certain environments have proved to be more challenging for the successful deployment of an RFID system. For example, in certain environments, a number of RFID readers and RFID tags may be utilized within a close proximity, resulting in a “noisy” radio-frequency environment in which a great deal of interference between competing signals may exist. Furthermore, RF noise and interference may be introduced into a particular operating environment by other devices (e.g., cellular or mobile telephones, microwave devices, etc.). Also worth noting is that different geographic locations may be subject to different radio-frequency transmission regulations. For example, in North America, for ultra-high frequency (UHF) RFID systems, (i.e., frequency hopping RFID systems utilizing the unlicensed 900 MHz radio-frequency band), regulatory restrictions allow for 50 or more channels, each channel being up to 500 kHz wide, and require that RFID readers must hop to a new channel at least every 400 ms. Furthermore, reader synchronization is disallowed. On the other hand, in Europe only 10 channels are allowed by the proposed ETSI 302 208 standard, each of these channels being 200 kHz wide, and RFID reader synchronization is allowed.
In short, it will be appreciated that a number of technical challenges exist with respect to the wide variety of environments, and associated environmental conditions, within which RFID systems may be required to operate. U.S. Pat. No. 5,649,295 to R. Anthony Shober, entitled document “DUAL MODE MODULATED BACKSCATTER SYSTEM” describes, as indicated by the title, a dual mode backscatter system. This document, in the background section, discusses the undesirability of a “single-mode” RFID tag that is capable of operating at either long-range mode or at higher bit rate mode, rather than being capable of operating in both modes. The document then goes on to describe a tag unit of an RFID system that has the capability to operate in a “dual mode” fashion. Specifically, a tag, based on a command from an interrogator, responds to the interrogator with either a “single tone” acknowledgement (to achieve great range) or with an information signal (for greater data rates at lesser range). The RFID system is further described in this patent as having the ability to communicate using the well-known Time-Division Duplex (TDD), Half Duplex or Full Duplex techniques.